1. Field of the Invention
The present invention relates to assemblies and systems for inspecting patterns of photomask and methods of performing an inspection process. More particularly, embodiments of the present invention relate to fine resolution inspection of photomasks.
2. Description of the Related Art
A photomask or reticle (hereinafter referred to as a photomask) can be used to transfer an optical pattern image onto a semiconductor substrate when the semiconductor substrate is manufactured. Because patterns of semiconductor devices are formed by using a photomask, forming fine optical patterns on the photomask is desirable.
In order to form fine optical patterns on a photomask, it may also be desirably to inspect the patterns formed on the photomask for defects.
As patterns formed on photomasks become finer, the resolution of systems for inspecting patterns of photomask may be increased to detect defects of the pattern. To obtain high quality resolution, the wavelength of light used in inspecting patterns may also be made relatively small. However, an inspection system with fine resolution typically takes a longer amount of time to inspect a sheet of a photomask. For example, when the length of the side of a unit pixel is reduced by one half (e.g. from 1 μm to 0.5 μm), the amount of time needed to inspect one sheet of a photomask increases by four times.
In comparison with typical systems for manufacturing a semiconductor (including photolithography), systems for manufacturing and inspecting a photomask are more expensive than other systems used for manufacturing a semiconductor. In addition, the process of inspecting a photomask is typically performed in steps after the sheet of a photomask is divided into a number of pixels, which can take a longer time than in other manufacturing process step. If all of the processes of inspecting a photomask are performed by a fine resolution system, more systems for inspecting patterns of a photomask may be provided to keep up with other manufacturing, which increases costs for quality control/review.
Fine resolution inspection systems may increase costs by using additional inspection lines and/or increase labor and other costs for operating and maintaining the inspection line. Accordingly, the introduction of fine resolution systems for inspecting patterns of photomask can be complex and potentially expensive.